Spring Stay Puzzle

[billknny]

When I first purchased my ketch the spring stay was installed with a single insulator more or less half way between the main and mizzen masts. Obviously not to use the wire as an antenna, no radio had ever been installed and a single insulator would not be much use for that application.

Anyone have a clue whey this might have been done? My guess is some lightning protection theory I am unfamiliar with.

In a related question, I do intend to install an SSB and need an antenna. A split backstay on the main makes an antenna installation there a bit tough. No permenent backstays on the mizzen eliminate that as a choice as well. In alternatives I have seen the spring stay can be used, though I worry a bit about the long lead up the mizzen. Another alternative I heard mentioned is to use a mizzen shroud. Is there a good, reliable way to insulate the shroud from the spreader tip?

Bill Kinney
http://www.geocities.com/bill_knny
S/V Fetchin' Ketch
Sausalito, CA

[Russ L]

Hi Bill,
Consider using a wire segment in the mizzen top'n' lift. A rope connection (or splice) at the top, around the sheave and drop to deck for adjustment. The lower end is also insulated (via rope?) to the boom and the antennea lead is fixed to the lower end of the wire.
Alternatively you could dead-end the upper end and have the adjustment lead at the lower end to save a bit o' weight aloft.
I believe you will have better radio performance with the antennea more vertical.
How about trying one of these gizmos and report back to us:
http://www.splicingnut.com/

I have no affiliation to splicing nut (but maybe I are one).

Cheers, Russ L

[billknny]

An interesting idea, Russ. Especially since I already have the wire topping lift for the mizzen in place. I am not sure that I like the idea of running the antenna lead out the mizzen boom, however. Not sure I don't like it either. Food for thought! I worry about flex and fatigue. Exactly how to manage the connection to the topping lift wire is where I am scratching my head. When the sail is hoisted, the topping lift does flop around a bit.

Anyone know if a line wet with salt water would be too conductive to work as an insulater for this application? I suspect so, but suitable insulaters for wire the size of my mizzen toping lift would be rather inexpensive.

Originally Posted by Russ L

Hi Bill,
Consider using a wire segment in the mizzen top'n' lift. A rope connection (or splice) at the top, around the sheave and drop to deck for adjustment. The lower end is also insulated (via rope?) to the boom and the antennea lead is fixed to the lower end of the wire.
Alternatively you could dead-end the upper end and have the adjustment lead at the lower end to save a bit o' weight aloft.
I believe you will have better radio performance with the antennea more vertical.
How about trying one of these gizmos and report back to us:
http://www.splicingnut.com/

I have no affiliation to splicing nut (but maybe I are one).

Cheers, Russ L

[Brion Toss]

Hello,
As I understand it, the best radio performance comes with a horizontal wire, which is why you'll see them rigged that way on large power vessels. But it's hard to do that on a sailboat, so we usually put them on the backstay, which at least leads at an angle, and only go to verticals, like portions of shrouds, if there's no backstay available, like on a gaffer. The vertical runs are also on the short side, as well.
An antenna on the mizzen lift would have the wire running the length of the boom, which would be bound to introduce major harmonics, unless it were wood. And if it were wood, that's still a long run: boom length; to deck (with flexing in the mix), and thence somehow to the tuner. Nah.
I have had clients put the tuner at the top of the mizzen, and then insulate the springstay. If it's a sufficiently compact, weatherproof tuner, it can work nicely. But I'm usually inclined to insulate the backstay pendant, and then bring the wire down one leg, being careful to avoid any run parallel to the leg (harmonics avoidance). It's a long run on a ketch, but the antenna is higher and longer than on the mizzen, and more angled than on a shroud. You have the option of insulating both legs, but there are likely only negligible gains there.
Fair leads,
Brion Toss

[Russ L]

Hello all,
I have learned that radio antennae choice is fraught with compromise, not unlike choosing a suitable sailboat.
The long wire horizontal radio antennae is considered a good performer, however it is directional. There is little practical radiation from the ends, so your best transmission is to the sides (beam to) and above. The long wire should be at least a half wave, and should be that distance above ground, so getting it 30 feet above the ground plane on a sailboat is easily done. The lead is part of the antennae length and since a tuner has better performance "making the wire longerî we should use a shorter than ideal antennae. So to maintain any kind of performance we need the tuner near the end of the long wire (top of mizzen).
The long wire horizontal antennae is not the best choice for a sailboat in transit or swinging on the hook.
I believe a dipole antennae to be impractical for the spring stay. It has the advantage of a coaxial lead but it is usually tuned for a specific band. The coaxial lead will usually fall from the middle of the antennae, as such it will foul the mainsail. The dipole consideration may explain the insulator in the middle of the spring stay, Bill.
A vertical antennae is omni directional. The broadcast area is greater so you need to optimize antennae efficiencies. This is your best choice for a system on the move. (Think VHF radio.)Ö and a boat offers a great ground plane.
A backstay antennae is kinda in between the two but much closer to vertical characteristics. However, a mainmast backstay antennae on a ketch rig with aluminum masts and wire shrouds surrounding it would be severely limited and not come close to the efficiencies that we require of a near vertical antennae.
Which leads me to the recommendation of a wire topping lift antennae on a ketch rig. It is near vertical and clear of the worst interference.
The best arrangement of this configuration should be a topic of much discussion. Two possibilities are: tuner up high on the mizzen or down near the boom. The upper placement of the tuner allows for a short lead length but is a top-loaded antennae and I have no idea of the effect on efficiencies of top-loading. The lower tuner placement allows for better sailing performance, but the lead along the boom lowers the antennae efficiency.
The details are the easy part. Isolating the antennae can be commercial or shop made items (as the load is low compared to standing rigging). The power loading of the antennae lead is not high so good quality wire is up to the task. There are many steel sloops cruising around with the tuner inside and the lead traveling under a side deck and out to the backstay. Topping lift movement (whipping around when the sail lifts the boom) can be countered with a section of bungee lashed to the wire & boom. I did this as a matter of course on the main (cutter rig) to limit chafe on the sail.
Cheers, Russ

[Renoir]

Your insulator can facilitate a dipole drive. A balun is installed to hang below the insulator, the coax is installed so as to angle back towards the mizzen to clear the main roach, barely. The compromise is to not have the coax downlead perpinducular to the beginning of the dipole yet, as has been pointed out, all sailboat antenna installations are compromises. The proof is whether or not the final installation works well or not. The dipole length consists of the spring stay plus the mizzen and main masts (assuming both are aluminum).

For 35 to 50 ft boats the installation may yield dipole dimensions which happen to work well on the 20 and 40 meter bands. If the dimensions are too small for these useful bands then small air inductors are placed in series with the balun output wires to the insulated leads tuned to give the correct performance. If the dimensions are too large capacitors are placed (selected to give the correct response) in series with the balun output leads. Obvouosly it takes two people using a noise bridge and an SSB receiver to achieve the tuning in place (who know what they are doing).

When done correctly the performance can be outstanding. Brion is correct in that most fixed receive long distance (DX) antennas are horizontally polarized and, therefore, for direct radiation from a transmit antenna, a horizontally polarized signal helps to maximize receive signal to noise ratios. Such compromise dipole installations typically have side lobes almost equal to the two direct lobes giving you four quadrants of directional transmission such that the lobes essentially touch each other yielding an overall omni-directional capability.